A particular example of the use of such nitrogen gases is the conventional use of nitrogen containing 10 v.p.m. of oxygen in gas chromatography. In gas chromatograpy the nitrogen is a carrier gas and oxygen if present can react detrimentally with the adsorbent materials used in the separation column. The quantities of nitrogen required are usually about 100 c.c./min. and this is usually provided by a cylinder of high purity nitrogen made by the conventional cryogenic process. The purpose of this invention is to provide a low cost alternative to cylinder high purity nitrogen by the production of nitrogen from a source of compressed air. A suitable adsorbant material for the separation of nitrogen from air is produced by Bergwerksverband GmBH, of Frillendorferstrasse 351, Essen, West Germany. The material is an activated coke in which the pore sizes have been modified so that a separation of oxygen and nitrogen can be made since the oxygen molecule is slightly smaller than the nitrogen molecule. The method of production of this special activated coke known as a carbon molecular sieve is documented in several U.K. patents as is the Bergwerksverband process enabling nitrogen to be produced. A particularly relevant Bergwerksverband patent is GB No. 1541767.
In this patent the use of two adsorbent columns is described and oxygen levels in the produced nitrogen are in the range of 0.1 to 3% oxygen.